High-power, single-mode laser diode sources are employed in a wide variety of applications. Exemplary applications include optical pumping of fiber amplifiers and solid state lasers, non-linear optical wavelength conversion and optical printing.
A variety of laser diode structures are known. Salient features of any given laser diode structure include: high output power, single near-Gaussian spatial mode, short- and long-term lasing mode stability over time, long-term reliability, compact packaging, manufacturability, and ease of coupling to an external waveguide such as an optical fiber. However, no single laser diode structure known possesses all of the above-described features.
Obtaining relatively high output power with single-mode emission by a laser diode is difficult. Structures having greater output power tend to produce either (a) multi-mode emission or (b) low long-term stability and reliability problems.
Some high-power, semiconductor laser diodes utilize a device structure referred to as a master oscillator power amplifier (MOPA). The MOPA light source referred to as a “master oscillator” or “injection laser” is optically coupled to a high-gain optical amplifier. MOPA lasers can be used to increase the output power of single mode lasers while maintaining a narrow linewidth. MOPAs use a structure having an oscillator section which produces a very narrow spectral output, and an integrated power amplifier section that increases the output power of the overall device without significantly affecting the spectral width. In some cases, the master oscillator and a high-gain optical amplifier are formed onto a common semiconductor substrate. However, for very high power applications, the master oscillator is formed on a first chip and the high-gain optical amplifier is formed on another chip. Such a MOPA, usually referred to as “Hybrid MOPA”, allows the MO and PA to be separately optimized unlike monolithic MOPAs.
One common problem with the two-chip MOPA arrangement based on conventional edge-emitting diodes is the coupling of light from the master oscillator to the high gain amplifier, which typically requires precise alignment on the order of several microns which may not be obtainable using conventional assembly processes. Thus, in this hybrid multi-chip embodiment coupling of light from the master oscillator to the high gain amplifier generally limits the obtainable performance of the MOPA. What is needed is a manufacturable hybrid MOPA coupling arrangement that facilitates assembly thereof to provide enhanced optical coupling between the master oscillator and high-gain optical amplifier.